JP2006500227A - Spring collet for machine tools - Google Patents

Abstract

The width λ of the spring collet joint ring (2) with the machine tool axis (1A) is determined as a function of the path of the clamping sleeve (20) where the spring collet stays at least partially. This width is preferably in the interval between 3 mm and 9 mm. The face (4; 4A; 4B) of the joint ring (2) exhibits a straight, curved or at least partly curved, inclined contour. The inclination angle formed by the axis (1A) is advantageously about 45 °. The spring collet (1) includes grooves (11; 12), the quantity of which may be greater than 3. The gaps between these grooves are determined so that the two opposite faces of each groove part (12R) touch each other when the spring collet (1) is in the closed position with respect to the workpiece (10) according to a predetermined clamping force. There is a possibility that.

Description

  According to the preceding part of the independent claims 1 to 8, the invention relates to a spring collet for machine tools, in particular for automatic lathes.

Disclosure

  Although this collet is designed to be mounted within the spindle of a machine tool, it is used for machining cylindrical workpieces intended for a very wide variety of applications. By way of example only, it may be used for machining shafts used for osteopathy, or shafts for micro motors. The front portion of the collet includes a tapered portion extending by a protrusion, presents at least two grooves that open toward the front end along a defined length, and has at least two clamps around the central opening Allows holding of a workpiece that is machined to form a jaw, so that the symmetry plane of each groove passes through the collet axis of rotation. In fact, all such collets currently commercially available have three grooves. The user owns an entire set of spring collets and has a spring collet suitable for that of the workpiece to be machined (about 1-10 mm diameter) (eg in a rework spindle or index attachment) In). During clamping, the clamping jaws grip the diameter portion of the workpiece as long as there is a gap between the respective groove faces. The length of the tapered portion of the groove known from the prior art is relatively long, but the apex angle of the column is about 30 °. Spring collets known to date have double drawbacks in terms of the variety of workpieces from the machining in which they are used.

  First of all, in many cases, the diameter of the workpiece varies along its length. The diameter difference between the central openings of these collets in the open position (maximum opening) and closed position (ie tightening to the workpiece) is very small (in the best case around 0.30 mm), and the workpiece to be processed Is often smaller than the diameter difference given. Therefore, it has an overall diameter D,-when the collet clamping jaws (intended to clamp workpieces of diameter D) are in their maximum open position-over a certain length, D + 0.40 mm The passing of the present workpiece is hindered. In such a situation, it is necessary to proceed in several stages in order to carry out the whole machining. This can include, for example, reworking the workpiece with a conforming sleeve, counter operation, etc., resulting in a significant increase in manufacturing costs.

  Secondly, in not a few cases, the manufacturer may characterize the workpiece or specify certain parameters related to machining data (workpieces made of relatively soft material, grasping of threads, thin walls ( Tube-shaped workpieces), the diameter of the workpiece at the clamping position, and the force applied to the workpiece by the cutting tool) face the danger of crushing the workpiece when the workpiece is clamped in the collet. The means currently used to limit the clamping force (for example, limit stop machining at some point in terms of limiting the path of the sleeve where the collet stays) is quite inadequate. The inability to control the clamping force is another source of increased manufacturing costs, while the number of work rejections remains high and the machining quality remains fairly inconsistent.

  The object of the present invention is to achieve the above two drawbacks (a very limited range of diameters of the central opening of all collets in a set and the risk of crushing the workpiece elements)-or the workpiece to be machined To achieve a spring collet that overcomes at least one or the other of those elements in each case in terms of the fact that depending on the type of piece, one or both of these disadvantages may be present .

  This object is achieved with respect to the measures as defined in independent claims 1 and 8, in which case claim 9 is concerned with all possible combinations thereof.

BEST MODE FOR CARRYING OUT THE INVENTION

  The following description presents various embodiments of a spring collet according to the present invention, in a non-limiting manner, by way of example only, with the aid of the accompanying figures.

  Note that the scale of the drawings is not uniform.

  FIGS. 1 and 2 show a spring collet 1 incorporated in an assembly (which forms part of a rework spindle), connected to the clamp piston 40 (right of the figure—ie behind the spring collet 1). It includes a clamp sleeve 20, a fixed sleeve 60 fitted with a roller bearing 70, a clamp nut 30 (left of the figure—that is, the front face of the spring collet 1), and an elastic member 50. The elastic member leans against the surface (not shown) of the sleeve 20 on one side and leans against the back surface 19 (shown in FIG. 3) of the spring collet 1 on the other side. After introducing the spring collet 1, the nut 30 is screwed into the threaded portion 61 of the sleeve 60. The joint ring 2 of the spring collet 1 is captured between the inner surface 33 of the hook 31 of the nut 30 and the front surface 21 of the sleeve 20, and the inner surface 32 of the nut 30 leans on the same surface with respect to the front surface 62 of the sleeve 60. ing. In this way, the spring collet 1 constitutes an integral part of the assembly.

  The spring collet 1 has a generally cylindrical shape in the sense that its axis is indicated by 1A and consists of a hollow body (see FIG. 3, in the figure it is an axial section in the closed position). Represented). From the joint ring 2 is tapered according to the example shown, extending from the base 3 (facing forward) and the horizontal tapered surface 4, with a protrusion 5 on one side and a span on the other side 6 and the rear part 6A of the span 6 remains guided by the clamp sleeve 20 (see also FIGS. 1 and 2), the outer diameter of the span being, according to its construction, a few more than the diameter of the protrusion. It extends over a range of millimeters. The hollow inner space consists essentially of the variable opening 7 and the notch 8. Around the central opening 7, according to an embodiment, a carbide insert 9 is provided which is applied to the workpiece 10 (FIGS. 1 and 2). The spring collet 1 includes three blind grooves 11, 12 according to this example, with the grooves 11 (FIG. 4) and 12 (FIGS. 5 and 6) corresponding to two different embodiments, respectively. Each pair of median planes 11P; 12P of the grooves 11; 12 forms an angle of 120 ° (shown only once in FIG. 4). These grooves 11; 12 open in the front towards the face 18 of the spring collet 1 and have three clamping jaws 14; 15- or more generally as many clamping jaws as there are grooves. Finishes forming, whereby the clamping jaws open and close by their elasticity. At the other end, the grooves 11; 12 open towards the hollow part 13 which allows the improvement of the elasticity.

  Returning to FIGS. 1 and 2, the spring collet 1 may be understood to open when the piston 40 is retracted backward; the clamp jaws 14; 15 themselves move away from the axis 1A of the spring collet 1, and the workpiece 10, while the spring collet 1 remains held between the nut 30 and the sleeve 20, and the elastic member 50 is connected to the inner surface 33 of the hook 31 of the clamp nut 30 as described above. It is understood that the tapered surface 4 of the joint ring 2 remains stationary on the same plane with respect to the front surface 21 of the clamp sleeve 20 in the middle of the opening. . The surface 21 corresponds to the surface 4 and is itself tapered and exhibits the same conicity as the surface 4 as the embodiments described in FIGS.

  When the spring collet 1 transitions from the open position (FIG. 2) to the closed position (FIG. 1) or vice versa, the sleeve 20 moves forward (or backward) as indicated by the letter c in FIG. It moves along the specified axial path (movement of the front face 22 perpendicular to the axis 1A). It is noted that this path is a function of the characteristics of the machine tool in the spindle on which the spring collet is mounted, and in practice the most typical value of c falls between approximately 1 mm and 3 mm.

  Due to the constraints imposed by this very limited path c, and the known spring collet ring structure (conicity on the order of 30 °, ie half the apex angle on the order of 15 °) and greater than about 15 mm From the viewpoint of (length in the axial direction), the problem (first defect) described in the introductory part of this specification is easy to understand.

  This problem is solved by means relating to the structure of the splice ring 2, which will be described further below.

  The axial length of the joint ring 2 (represented by the letter λ in FIG. 3) is determined by a function of the path c. According to the present invention, this equation is such that the length λ can be selected within an interval limited by approximately twice (lower limit) c and 5 times (upper limit) c. Since it is known that the normal value of the path c of the sleeve 20 ranges from approximately 1 mm to 3 mm, the length λ falls within a range extending between approximately 2 mm and 15 mm. Experience has shown that the axial length λ of the joint ring 2 is advantageously between 3 mm and 9 mm, depending on the diameter for which the spring collet is intended. It is the latter conicity (half angle α and axis 1A) determined by the length λ and by the diameter of the span 6 of the sleeve 20 at the intersection 2B of the sleeve and the tapered surface 4. And busbars included in the plane supporting line segment 2A-2B (respectively the base of the cone of the joint ring 2 and the intersection), in the context of the span 6 diameter range allowed by the configuration, The selected angle α indicates that in all cases it must be greater than 15 °.

  Naturally, as the conicity becomes more prominent, the value λ approaches the lower limit, and the force that the piston 40 must apply to the joint ring 2 by the sleeve 20 increases. As a result, the risk of damaging the joint ring increases. Accordingly, the selection of the minimum value of λ and the maximum value of angle α is limited by constraints imposed by the construction of the joint ring 2 and the properties of the composition (material). Experiments show that the angle α does not exceed 75 °, but shows that the inhibitory properties become stronger as α approaches 90 °. According to the embodiment represented by FIGS. 1, 2 and 3, the angle α of the tapered portion of the joint ring 2 is expediently 45 °.

The contour of the back side surface of the joint ring is curved or with (contour 4A in FIG. 7 or at least one planar portion (contour 4B in FIG. 8, where the planar portion is indicated by line segment 4M). The entire inclined portion of the surfaces 4A, 4B is uniformly represented by a reference bus 4P, which is the right hand segment 2A-28 (as shown in FIG. 3). And the buses form angles α _A and α _B , respectively, with the axis 1 _{A. Of} course, the corresponding surface of the sleeve 20 (not shown in FIG. 7) exhibits a similar contour each time. This configuration has the advantage (advantage) of better distribution of the force on the joint ring 2, but in order to produce the same effect-i.e. to obtain the same opening of the clamping jaws 14; 15. -The pressure that needs to be applied to the latter is Less made it to.

  The second means can be combined with the above, but consists of increasing the number of grooves 11; 12. The maximum number of grooves is determined by a function that takes into account machine aspects of construction and / or manufacturing. This increase again makes it possible to reduce the force that must be applied to the joint ring 2 in order to obtain the same opening of the clamping jaws 14; 15. In the measurements made on a spring collet given the above means (even if the second means is not applied), the difference between the opening position and the opening position (for illustrative purposes only) below: Makes it possible to achieve: 0.6 mm for spring collets provided when clamping workpieces with a diameter of 1 mm (maximum opening is 1.60 mm), 1.1 for spring collets for 6.25 mm workpieces. The spring collet for the 25 mm and 10.00 mm workpieces was 3.00 mm. When imagining a workpiece 10 (see FIGS. 1 and 2) with a clamp diameter 10A of 1.00 mm, 6.25 mm or 10.00 mm, confront the operator with a type of problem that requires ancillary operations. Instead, each of the diameters 10B and 10C can be 1.60 mm, 7.50 mm, or 13.00 mm.

  The second drawback is solved according to the present invention by modifying the groove shape (FIGS. 5 and 6). Generally, when the spring collet 1 is in the closed position (ie, when the workpiece is tightened), a gap remains between the opposing surfaces (not shown) of each groove 11 (FIG. 3). Increasing the clamping force remains possible. The above correction is determined in each particular case as a function of the above detailed parameters (tubular workpiece, presence of screwing, etc.). In other words, for permissible—ie pre-calculated—clamping forces, the gap between the grooves is corrected taking into account the parameters (FIG. 5 with the spring collet in the open position and the spring collet (See FIG. 6 in the closed position). This correction consists of giving the groove 12 a gap ε, at least a radial distance defined for it (shown by reference 12R for one of the three grooves in FIG. Towards part 7 and partly towards notch 8 (FIG. 3)). The gap ε is such that when the spring collet 1 is in the closed position (FIG. 6) and a predetermined clamping force is applied to the workpiece to be machined in this way, the opposing surfaces of the groove 12R portions are in close contact with each other, As a result, it is calculated in a way that does not allow any increase in clamping force on the workpiece being machined. In this way, the workpiece will be protected from any damage due to unintentional crushing.

FIG. 2 is an axial cross-sectional view of an assembly with a spring collet mounted therein, with the collet shown in a closed position. FIG. 2 is an axial cross-sectional view similar to that shown in FIG. 1 with the collet shown in an open position. It is an axial sectional view of only a spring collet. FIG. 3 is a side view of a spring collet (in the closed position) showing the shape of a groove according to one embodiment. FIG. 6 is a side view of a spring collet (respectively in an open and closed position) showing the shape of a groove according to another embodiment. FIG. 6 is a side view of a spring collet (respectively in an open and closed position) showing the shape of a groove according to another embodiment. Fig. 5 shows the deformation of the contour of an element with a spring collet. Fig. 5 shows the deformation of the contour of an element with a spring collet.

Claims (9)

  Spring collet for machine tools, in particular for automatic lathes, presents a central opening in the shaft (1A) that can be changed from an open position to a closed position to release and stop the workpiece (10), and has at least two The groove (11; 12) and the corresponding surface (21) of the sleeve (20) include a joint ring (2) on the leaning surface (4; 4A; 4B), which allows the open and closed positions. So that it can translate forward and backward along a limited axial path (c), with the axial length λ of the splice ring (2) being about twice the minimum and maximum limits of c and c The surface (4) exhibits an inclination (4; 4P) of more than 15 ° relative to the axis (1A) of the spring collet 1. A spring collet.   2. The axial length λ of the joint ring (2) may be selected within a spacing of approximately between 2 mm and 15 mm, and the path c is located in a range between approximately 1 mm and 3 mm. Spring collet.   3. Spring collet according to claim 1 or 2, wherein the axial length [lambda] of the joint ring (2) is clearly located within a distance of between approximately 3 mm and 9 mm.   The spring collet according to any one of claims 1 to 3, wherein the inclination (4; 4P) is about 45 °.   The spring collet according to any one of claims 1 to 4, wherein the contour of the inclined surface of the joint ring (2) is straight or at least partially curved. The spring collet according to any one of claims 1 to 5, wherein the number of grooves (11; 12) included in the spring collet exceeds three.   The spring collet according to any one of claims 1 to 6, wherein the difference in diameter between the open and closed positions exceeds 0.30 mm.   Spring collet for machine tools, in particular for automatic lathes, presents a central opening of the shaft (1A) that can be changed from an open position to a closed position to release and block the workpiece (10), and has at least two The groove (11; 12) and the corresponding surface (21) of the sleeve (20) include a joint ring (2) on the leaning surface (4; 4A; 4B), which allows the open and closed positions. So that it can be translated forward and backward along a limited axial path and at least one portion (12R) of the groove (12) is spring collet (1) when the spring collet (1) is in the open position. When 1) is in the closed position with respect to the workpiece (10) according to a predetermined clamping force, the two opposite faces of each groove part (12R) are in contact with each other. Characterized in that exhibits a gap 8 that is, the spring collet.   The spring collet according to claim 8, comprising the features of any of claims 1 to 7.

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